1. Field of the Invention
The present invention relates to a fuel cell unit formed by stacking a rectangular membrane electrode assembly and a rectangular separator together, the membrane electrode assembly containing a pair of electrodes and an electrolyte membrane interposed between the electrodes. The membrane electrode assembly also includes a picture-frame-like resin frame formed on an outer circumference thereof. Further, the present invention relates to a fuel cell formed by stacking a plurality of such fuel cell units.
2. Description of the Related Art
For example, in a solid polymer electrolyte fuel cell, an electrolyte membrane composed of a polymer ion exchange membrane is interposed between an anode and a cathode to form a membrane electrode assembly (MEA). The membrane electrode assembly is sandwiched between separators to form a fuel cell unit. In use, generally, a predetermined number of such fuel cell units are stacked together to form a fuel cell stack, which is mounted in a vehicle, for example.
In general, several tens or hundreds of the fuel cell units are stacked to obtain the fuel cell stack. In the stacking process, it is necessary to accurately position constituent members of the fuel cell unit to each other and the fuel cell units to each other. For example, a solid polymer electrolyte membrane fuel cell disclosed in Japanese Laid-Open Patent Publication No. 2000-012067 is known.
As shown in FIG. 27, this fuel cell includes a unit cell 3 formed by sandwiching a cell (electrolyte-electrode assembly) 1 between separators 2A, 2B, the cell 1 including an electrolyte layer 1A, and a fuel electrode 1B and an oxidant electrode 1C which sandwich the electrolyte layer 1A therebetween. A holding pin insert hole 4a, a retaining ring insert hole 4b, and a hole 5 are coaxially formed in the separator 2A, the separator 2B, and the electrolyte layer 1A, respectively.
A holding pin 6 is inserted into the holding pin insert hole 4a, the hole 5 and the retaining ring insert hole 4b. A retaining ring 7 is attached to a distal end of the holding pin 6, whereby the unit cell 3 is integrally retained. A pin-distal-end insert hole 8 is formed in a rear end portion of the holding pin 6, and the distal end of the adjacent holding pin 6 is inserted thereinto in the process of stacking a plurality of the unit cells 3.
Meanwhile, in the case where a metal separator obtained by forming a thin metal plate into a corrugated shape is used as a separator of the fuel cell, when grooves for a fuel gas flow field are formed on one surface of the anode-side metal separator, ridges corresponding to the reverse side of the grooves are formed on the other surface thereof. Furthermore, when grooves for an oxygen-containing gas flow field are formed on one surface of the cathode-side metal separator, ridges corresponding to the reverse side of the grooves are formed on the other surface thereof.
For example, Japanese Laid-Open Patent Publication No. 08-222237 discloses a fuel cell stack, which is formed by stacking a plurality of cells (fuel cell units) containing a solid electrolyte and electrodes disposed on opposite sides of the solid electrolyte. In the fuel cell stack, a fuel cell separator is interposed between the adjacent cells. On one surface of the separator, fuel gas flow grooves for supplying a fuel gas to one of the adjacent cells are formed, and on the other surface, oxygen-containing gas flow grooves for supplying an oxygen-containing gas to the other of the adjacent cells are formed.